Magnetic media in the form of tapes or disks have been widely used for storage of information. Magnetic heads are commonly employed for the tasks of interacting with these magnetic media for information storage and retrieval. As is well known in the art, a magnetic head comprises an inductive coil sandwiched between a pair of magnetic poles. During the data writing mode, the current carrying coil induces magnetic flux into the magnetic poles, which in turn magnetize a moving recording medium disposed close to the magnetic head. Similarly, during the data reading mode, magnetic flux emanating from a recording medium is intercepted by the magnetic poles, which in turn induces electrical current in the inductive coil. The induced current in the coil corresponds to the information stored in the recording medium.
Operations of the aforementioned types of magnetic head are subject to various problems. One significant problem is Barkhausen noise that is encountered during the reading and writing processes, which noise arises mainly from magnetic domain instability in the magnetic poles. Each magnetic pole in the magnetic head assumes a certain magnetic domain pattern at its quiescent state. During the data writing mode, write current flowing into the coil induces magnetic flux which traverses the pole. The Joule heat generated by the write current is sufficient to cause considerable thermal expansion in the magnetic pole and the surrounding dielectric material. Since the coefficients of thermal expansion are different between the magnetic pole material and the dielectric material, thermal stress is thereby created. In response, the original domain pattern is altered into a different pattern. Upon the withdrawal of the write current at the end of the writing process, the altered domain pattern again changes in an effort to recover itself to its original pattern. This time, the domain pattern changes relatively sluggishly and correspondingly induces electrical noise in the inductive coil. The noise so induced, is commonly called popcorn noise or Barkhausen noise. The occurrence of popcorn noise during normal operations is detrimental to the performance of the magnetic head.
It should be noted that the emerging of popcorn noise in magnetic heads is highly unpredictable. Some magnetic heads are more prone to generate popcorn noise than others. However, there appears to be a strong correlation between the propensity of popcorn noise in a magnetic head and the fabrication process. That is, there are lot-to-lot differences with regard to popcorn noise susceptibility in the magnetic heads resulting from manufacturing. A well-controlled manufacturing process could screen out magnetic heads with sub-standard performance. However, a testing tool capable of detecting popcorn noise in the magnetic heads with accuracy must first be provided.
Heretofore, no optimum systematic approach for detection of popcorn noise in magnetic heads has yet been devised. A typical test setup involves linking different signal generators and measuring equipments together. As arranged, popcorn noise events are normally observed and counted through the display of an oscilloscope. The main drawback of such an approach is the lack of accuracy. Very often, externally generated noise masks out the actual popcorn noise intended to be detected. Moreover, monitoring of such testing system is a cumbersome endeavor. For example, a change in a measuring parameter would require a readjustment of different equipments. Accordingly, these test setups are inaccurate and especially not suitable for the production environment.